Cooling fan system for a vehicle with fuel cell propulsion

ABSTRACT

A cooling fan system for a vehicle with fuel cell propulsion, wherein air is moved by means of a cooling fan for cooling purposes through a heat exchanger and can thereafter be supplied to the environmental air either directly or indirectly after satisfying one or more further cooling tasks, characterized in that an air branching device is provided which supplies at least a part of the air delivered by each fan to a duct and thereby enables the use of the branched-off air for the starting of the fuel cells and/or for the maintenance of the operation of the fuel cells.

TECHNICAL FIELD

[0001] The present invention relates to a cooling fan system for avehicle with fuel cell propulsion, wherein air is moved by means of acooling fan for cooling purposes through a heat exchanger and canthereafter be supplied to the environmental air either directly orindirectly after satisfying one or more further cooling tasks. Theinvention relates furthermore to a method for the operation of a fuelcell system.

BACKGROUND OF THE INVENTION

[0002] Many proposals have already been made for the equipping ofvehicles with fuel cell propulsion systems. Such vehicles are alreadybeing constructed and tested.

[0003] With such fuel cell propulsion systems, the fuel cells deliverelectrical energy which, after appropriate processing, is applied to oneor more drive motors which take care of the propulsion of the motorvehicle.

[0004] For fuel cell propulsion systems for vehicles, PEM (ProtonExchange Membrane) fuel cells are currently preferred which areconnected in parallel and/or in series to one another and form aso-called stack. The fuel cells are supplied, on the one hand, withhydrogen from a suitable source. Protons which originate from thehydrogen and pass through the membranes of the fuel cells combine in thefuel cells with the oxygen of the air which is supplied to form waterwith the simultaneous generation of electrical energy.

[0005] The vehicle can be equipped with a hydrogen storage tank, andmay, however, also be fed with a synthesized hydrogen-rich gas which isobtained from a hydrocarbon such as methanol. In this case, thehydrocarbon is processed in a processing device in the form of aso-called reformer to form the synthesized hydrogen-rich gas. When areformer is used, it also requires air.

[0006] Fuel cells are also known which are directly fed with methanol,with the methanol consisting of up to 97% water. Such fuel cell systemsrequire oxygen for the power generating reaction and must be suppliedwith air by a compressor.

[0007] Independently of the type of fuel cells which are used, acompressor is always required which makes available the compressed airfor the fuel cells or for the reformer. Part of the output power of thefuel cell system is also applied to an electric motor which is requiredin operation to drive the compressor.

[0008] In practice, problems arise with the starting of a fuel cellsystem.

[0009] One known solution involves the use of a traction battery with,for example, 288 V operating potential. This traction battery has inprinciple three different tasks:

[0010] On the one hand, it is used to drive the main compressor in orderto feed air compressed by this compressor into the fuel cell system, sothat power is generated which then replaces the traction battery as thepower source for the electric motor driving the compressor.

[0011] The second task of the traction battery is to assist dynamicallythe electric motor or electric motors which propel the vehicle so that,for example, with fast acceleration or at elevated speeds, the power ofthe traction battery supplements the electrical output power of the fuelcell system.

[0012] The third task lies in the fact that a traction battery can beused in order to realize regenerative braking for example. That is tosay, on braking of the vehicle, the kinetic energy which is present ispartly converted into electrical energy which can then be stored in thetraction battery.

[0013] Although a traction battery can be useful for these differentpurposes, it represents an expensive and heavy component, so that onewould be pleased to dispense with it. If, however, the traction batteryis dispensed with, it could no longer be used to start up the fuel cellsystem.

[0014] For the starting of the fuel cell system, air is required. Theair compressor is normally driven from the fuel cell potential; however,this is not yet available. In the absence of a traction battery, it hasalready been proposed to supply the fuel cell system with sufficient airby means of a 12 V auxiliary fan, i.e., a so-called start-up blower, sothat the power generation starts there and the system can be graduallyrun up until the power generation by the fuel cell system is sufficientin order to maintain the system in operation.

[0015] Irrespective of whether one operates with a traction battery orwith an auxiliary blower, many components which make the system morecomplicated or more expensive, such as fans, radiators, pipes, 288 Vbatteries, etc., are necessary which one would prefer to do without.

SUMMARY OF THE INVENTION

[0016] The object of the present invention is to make sufficient airavailable so that the fuel cell system can be started and run up withoutusing a traction battery or an auxiliary fan.

[0017] In order to satisfy this object, provision is made, in accordancewith the invention, for an air branching device to be provided whichsupplies at least a part of the air delivered by each fan to a duct andthereby enables the use of the branched-off air for the starting of thefuel cells and/or for the maintenance of the operation of the fuelcells.

[0018] In other words, it has been recognized, in accordance with theinvention, when using a fuel cell propulsion system in which a coolingfan driven by the normal onboard battery is used for the cooling ofliquid flowing through a heat exchanger, with the throughflowing airalso being capable of being used for further cooling tasks, that thesystem consisting of the cooling fan and heat exchanger is unnecessaryper se during the starting of the fuel cell system, since the heat whichthen arises is restricted, and that the cooling fan associated with theheat exchanger can thus be exploited for the starting of the fuel cellsystem until the fuel cell system delivers sufficient power to drive thecompressor itself. That is to say, the cooling fan is used in the shortterm for the starting of the fuel cell system.

[0019] This can in principle take place in such a way that an airbranching device, which is simply formed by a fixed guide wall, isprovided and always branches off a part of the air flow produced by thecooling fan and supplies it via a suitable line to the fuel cells and/orto a reformer. On operation of the system, a device must then beprovided in order to close off the duct when the compressor starts torun in order to prevent the compressed air generated by the compressorfrom escaping through the corresponding duct in the form of a reverseflow. This need could indeed be avoided if the branched-off air flowgenerated by the cooling fan is supplied to the inlet of the compressorand thus via the compressor to the fuel cells and/or the reformer.

[0020] A further possibility is to make the air branching device movableso that it can be switched between a first substantially inactiveposition and a second position which brings about the branching off ofthe air. In this manner it is not only possible to use part of the airflow delivered by the cooling fan, but rather the entire air flow can beused for the starting of the fuel cell system.

[0021] The cooling fan can in principle be a suction fan which isarranged downstream of the heat exchanger and sucks the air through thelatter, with the air branching device then being arranged downstream ofthe suction fan. Such suction fans are customary with fuel cellpropulsion systems.

[0022] It is, however, more favorable if each cooling fan is a pusherfan which is arranged in front of the heat exchanger. A fan of this kindis better able to deliver the airflow required for the starting of thefuel cells because it operates more efficiently under backpressureconditions.

[0023] When using a pusher fan, it is preferably connected to the heatexchanger by means of a housing which avoids air losses.

[0024] It is particularly favorable when an air guiding housing isarranged downstream of the heat exchanger directly adjacent to thelatter so that all the air flowing through the heat exchanger entersinto the air guiding housing.

[0025] Various possibilities exist in accordance with the invention inorder to realize the air branching device. This can, in particular, berealized by adjustable plates, which, in a first position, permit theair moving through the heat exchanger to pass and, in a second position,close against one another in order to supply the air to the duct leadingto the fuel cells. The plates are preferably arranged at the downstreamside of the air guiding housing.

[0026] They can, for example, be arranged in the manner of a louverwindow. Another possibility is to arrange them in the manner of an irisdiaphragm, with the plates forming a central opening in the state closedagainst one another, which lies opposite to the entry to the ductleading to the fuel cells.

[0027] The possibility also exists of arranging the plates in the mannerof a roller shutter.

[0028] It is particularly favorable when an air collecting box extendsover a region of the air guiding housing which is not covered over bythe air branching device in the air branching-off position and collectsthe air deflected by the air branching device and directs it to the ductleading to the fuel cells. An air collecting box of this kind can bestraightforwardly used with an air branching device consisting ofplates, in particular if these are arranged in the manner of a louverwindow (Venetian blind) or in the manner of a roller shutter, since theair collecting box extends over the entire width of the heat exchangerand the plates can close against an edge region of the air collectingbox.

[0029] A further possibility for realizing the air branching device andto use it with an air collecting box is to form the air branching deviceas a roller blind.

[0030] Instead of using an air collecting box, the air branching devicecan in the second position fully close off the air outlet side of theair guiding housing and the latter can have a connection for a ductleading to the fuel cells. In this way, the need to use a separate aircollecting box is avoided, i.e., the air guiding housing, which is inany event present, is itself used as the air collecting box.

[0031] With embodiments utilizing an adjustable air branching device,the positioning motor for the positioning of the same is preferablymounted on the air guiding housing.

[0032] An air filter can be built into the air collecting box or intothe duct leading to the fuel cells in order to ensure that the fuelcells and/or the reformer are only fed with clean air.

[0033] It is particularly favorable that in the invention the coolingsystem consisting of the cooling fan and the heat exchanger with the airbranching device and the housings associated therewith, as well as anymotor for the positioning of the air branching device, can be built upas a module, since it can then be designed in a space-saving manner as aunit which is easily exchangeable and which can be manufactured atfavorable cost with a minimum of additional parts.

[0034] Finally, there is provided, in accordance with the invention, amethod for the operation of a fuel cell system comprising a heatexchanger with at least one fan which produces a cooling air flowthrough the heat exchanger and with the a fuel cell arrangement fed withcompressed air from a compressor, characterized in that at least a partof the cooling air flow is supplied to the fuel cell arrangement, andoptionally to a reforming device connected in front of the fuel cellarrangement, for the starting of the fuel cell system and/or for themaintenance of operation in low load ranges, for example, during idling,during loss of speed by rolling or during overrun operation.

BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The invention will be explained in more detail in the followingwith reference to embodiments and to the drawings in which:

[0036]FIG. 1A shows an exploded illustration of a cooling fan module inaccordance with the invention for a vehicle;

[0037]FIG. 1B shows a perspective illustration of the assembled moduleof FIG. 1A in which the air branching device is located in a firstoperating position in which no pronounced branching off of air takesplace;

[0038]FIG. 1C corresponds to FIG. 1B but shows the air branching devicein a second position in which air is branched off;

[0039]FIG. 2 shows a schematic side view of the module of FIG. 1C in aslightly modified form and connected to a fuel cell system;

[0040]FIG. 3A shows an end view of a further cooling fan module inaccordance with the invention with an air branching device in the formof an iris diaphragm in the closed, air branching position;

[0041]FIG. 3B shows a representation similar to FIG. 3A but with the airbranching device in the first, open position in which no branching offof air takes place;

[0042]FIG. 3C shows a side view of the embodiment of FIGS. 3A and 3B;

[0043]FIG. 4A shows an end view of a further cooling fan module inaccordance with the invention seen from the downstream side with an airbranching device in the form of a roller blind in a partly open state;

[0044]FIG. 4B shows a representation similar to FIG. 4A, but with theroller blind in the second closed position in which branching off of airtakes place;

[0045]FIG. 4C shows a side view of the cooling fan module of FIGS. 4Aand 4B;

[0046]FIG. 5A shows an end view of a further variant of a cooling fanmodule in accordance with the invention at the downstream side with anair branching device in the form of a roller shutter being used andbeing shown here in the closed state; and

[0047]FIG. 5B shows a representation similar to FIG. 5A, but in thefirst open operating state of the roller shutter.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0048]FIG. 1A shows in a perspective, highly schematic representation acooling fan module 10 consisting of two pusher fans 12 which press airthrough a heat exchanger 14 in order to cool a liquid, which is notshown but which flows through the heat exchanger 14.

[0049] An air guiding housing 16, here in the form of a rectangular box,carries a plurality of pivotally hinged plates 18 in the form of alouver window and covered over in the lower region by an air collectingbox 20, with the air collecting box 20 opening into a duct 22 which, inaccordance with FIG. 2, leads directly or indirectly to the fuel cells,as will be explained in more detail later. The plates 18 form an airbranching device 19.

[0050]FIG. 1B shows the module of FIG. 1A in the assembled state, and itcan be recognized that this is a compact, space-saving design. At theupper left-hand side of the air guiding housing, which is formed as aframe, there is a positioning motor 24 which is connected to theindividual plates 18 via a lever arm 26 and connecting rod 28 and whichcan move or pivot the plates from a first open operating position, inaccordance with FIG. 1B, in which at least substantially no branchingoff of air takes place, into a second closed position shown in FIG. 1Cin which the individual plates 18 close in an air-tight manner againstone another and against the air guiding housing 16, so that the airdelivered by the fans 12 is forced to flow into the air collecting box20 and this air passes from there via the duct 22 to the fuel cells.

[0051] In a simplified embodiment, the plates 18 and the motor 24 areomitted and the wall of the air collecting box forms a fixedly disposedguide wall forming the air branching device. A plurality of differentembodiments with fixedly arranged guide walls can also be considered.

[0052]FIG. 2 shows essentially the same design of the cooling fan moduleof the invention as in FIGS. 1A-1C, but with some differences. First ofall, FIG. 2 makes it clear that the two cooling fans 12 are connected tothe heat exchanger 14 via a housing 30, so that the total quantity ofair which is conveyed by the pusher fans 12 has to flow through the heatexchanger 14. In this example, the outlet 22 of the air collecting box20 is led out at the rear of the air collecting box and not at the sideas in the example of FIG. 1. The outlet 22 leads into a duct 32 whichleads to an air inlet 34 of the fuel cell arrangement 36. Within thefuel cell arrangement 36 there is in known manner an air distributionpassage to which both the air inlet 34 and the air inlet 38, which isconnected to the outlet of the air compressor 40, lead.

[0053] In the normal operation of the fuel cell arrangement, thecompressor 40 sucks in air via the inlet 42, with an air filter, forexample, being positioned upstream of the inlet 42, compresses the airand then delivers it as compressed air via the inlet 38 to the fuel cellarrangement 36.

[0054] In order to avoid an undesired reverse flow via the duct 32 onoperation of the compressor 40, the duct 32 is provided with a valveflap 44 controllable by a control 42. The valve flap 44 shown in theopen position in FIG. 2 can, however, be moved via the control 42 into aclosed position in order to prevent the aforementioned reverse flow.

[0055] A correspondingly controllable valve flap can also be arranged inthe region of the air inlet 38 or of the inlet 42 in order to preventair escaping via the compressor 40 when the fuel cell arrangement is fedby the pushed fans 12.

[0056] The valve flap 44 can be omitted when the duct is led, asindicated by 32′, into the air induction pipe 42 of the compressor. Theair inlet 34 of the fuel cell arrangement 36 is then superfluous. It is,however, eventually necessary to provide a valve in the region of theair induction tube 42 upstream of the mouth of the line 32′ in order toavoid an undesired loss of air here when operating the pusher fan priorto taking the compressor into operation.

[0057] The reference numeral 46 indicates an air filter which in thisexample is arranged in the duct 32. As an alternative, an air filter 46′could be accommodated in the air collecting box 20.

[0058] On starting a vehicle with the fuel cell system of FIG. 2, themotor 24 is first energized in order to close the louver plates 18,i.e., to bring them into the position of FIG. 1C. At the same time thevalve 44, if present, is opened and the pusher fans 12 operated by thelow voltage onboard battery are switched on so that the compressed airproduced by the pusher fans 12 passes via the housing 30, the heatexchanger 14, the air guiding housing 16, and the air collecting box 20into the duct 32 and thus to the fuel cells 36. Should the duct be leadinto the compressor inlet, as shown at 32′, the compressed air passesfrom the pusher fans via the compressor 40 into the fuel cellarrangement 36. At the same time, hydrogen or a synthesizedhydrogen-rich gas is supplied to the fuel cell arrangement 36 via thehydrogen inlet 48. The fuel cell arrangement 36 then starts to producepower.

[0059] As soon as the quantity of power which is generated is sufficientto drive the motor (not shown) which drives the compressor 40, thismotor is set operating. The compressor 40 then delivers the requiredquantity of air in order to keep the fuel cell arrangement 36 operatingand to produce the necessary power.

[0060] As soon as the compressor 40 delivers sufficient air to the fuelcell arrangement 36, the motor 24 can be controlled in order to bringthe louver plates 18 into the open position of FIG. 1B. The valve flapcan be brought into a position in which it closes the duct 32, so thatno air losses arise due to reverse flow via the duct 32. Instead ofusing an electrically controlled valve, i.e., instead of using a valveflap, this can also be designed as a non-return valve. This also appliesto a valve which may possibly be provided in the region of the inlet 38or in the air supply to the compressor 40, in order to avoid air losseson feeding the fuel cell arrangement 36 by the pusher fans 12.

[0061] Although an air collecting box is used in the embodiments ofFIGS. 1 and 2, one can dispense with such an air collecting box. Insteadof this, the air outlet 22 can be led directly out of the air guidinghousing 16 or out of the housing 30. The louver plates 18 or otherbranching off devices must then cover over the entire outlet side of theair guiding housing 16 or of the heat exchanger. When the air outlet isled out of the housing 30, the branching off device could be arranged infront of the heat exchanger and fully cover over its inlet side.

[0062] These further possibilities of placement of the air outlet areindicated in FIG. 2 by 22′ and 22″.

[0063] FIGS. 3A-3C show an alternative form of the air branching device.In this example, the air branching device 50 again consists of plate18′. These are, however, arranged in the manner of an iris diaphragm.FIG. 3A shows the closed position of the iris diaphragm. One notes thatthe radially inner ends of the plates 18′ form an open circular orifice52 which lies opposite to the inlet of an air collecting cone 54 (FIG.3B) provided with an outlet 22″′. The iris diaphragm is so designed thatthe radially inner ends of the plates 18′ directly sealingly contact theair collecting cone 54 directly adjacent to the opening, so that thecompressed air produced by the pusher fans 12 is collected by the aircollecting housing 16 and forced into the air collecting cone 54 fromwhich it passes via the air outlet 22″′ into a duct such as 32 or 32′.

[0064]FIG. 3B shows the fully-open position of the iris diaphragm whichbounds a circular, ring-shaped air outlet 56 for the air which passesthrough the heat exchanger 14. In this example, it can be advantageousto operate with only one circular pusher fan 12. In this example, theplates 18′ are moved by the motor 24′ between the positions of FIGS. 3Aand 3B. In a modified variant, the plates 18′ of the iris diaphragmcould close completely and an air outlet 22′ or 22″ could be provided asin the embodiment of FIG. 2.

[0065]FIG. 4 shows an alternative embodiment in which an air branchingdevice in the form of a roller blind 60 is used at the outlet side ofthe air guiding housing 16. This roller blind 60 is a flexible,impermeable membrane 62 which can be rolled up onto an upperspring-loaded cylinder 64, with the spring loading being so designedthat it endeavors to move the roller blind in the direction of the arrow66 into a fully-open position. At the lower side of the roller blind 60in FIG. 4A there are two cables 68 which can be rolled up onto acylinder 70 in the lower region of the air guiding housing 16, thecylinder 70 being driveable by a motor 72.

[0066] The motor 72 can unwind the roller blind 60 from the upperspring-loaded cylinder 64 by rotation of the cylinder 70 around the axis76 in accordance with the arrow 74, with the cylinder 64 being rotatablyarranged about its longitudinal axis 78.

[0067]FIG. 4A shows an intermediate position in which the lower edge ofthe roller blind 60 has started to cover over the air outlet side of theair guiding housing, whereas FIG. 4B shows the fully-closed position.

[0068] The motor 72 is used in order to bring the roller blinds 60downwardly into the closed position of FIG. 4B, where the blind can beheld by a non-illustrated latch, for example by a pin, which is actuatedby a solenoid. As soon as the fuel cell arrangement produces sufficientpower in order to drive the compressor 40, the latch is released, forexample by interrupting the supply of current to the solenoid, and thespring-loaded cylinder 64 then serves to wind up the roller blind sothat this moves back into the fully-open position (not shown).

[0069]FIGS. 5A and 5B show a similar arrangement except that here an airbranching device 84 is used with plates 18′ in the form of a rollershutter. In this example, the roller shutter is drawn downwardly viacables 68′ by a spring-loaded cylinder 80 in order to attain the closedposition of FIG. 5A in which the lowermost plate 18″ sealingly closesagainst the lower edge of the air collecting box 20. For the opening ofthe roller shutter, the motor 72 is energized. It then turns thecylinder 82 which rolls up the plates until the fully-open position ofFIG. 5B is reached. The roller shutter can then be held in this positionby a non-illustrated latch, so that the motor 72 does not need to bepermanently energized.

[0070] Although the device of the invention is primarily used for thestarting up of the fuel cell system, it could, under some circumstances,be used when it is only necessary to maintain the operation of the fuelcells, so that the vehicle can immediately start again when operating ina low load region, for example, during idling at a traffic light, inoverrun operation or when loosing speed by rolling. The possibility ofswitching off the motor for the compressor in these operating phases cancontribute to noise reduction.

1. A cooling fan system for a vehicle with fuel cell propulsioncomprising a plurality of fuel cells, a heat exchanger, at least onecooling fan adapted to direct a cooling air flow through said heatexchanger, an air branching device adapted to branch off at least a partof the cooling air flow delivered by said at least one cooling fan, aduct for receiving said branched-off air flow and for directing it tosaid fuel cells for the purpose of at least one of starting of the fuelcells and maintenance of the operation of the fuel cells.
 2. A coolingfan system in accordance with claim 1, wherein said air branching deviceis formed by a fixed guide wall.
 3. A cooling fan system in accordancewith claim 1, wherein said air branching device has a first position anda second position in which it brings about the branching off of air fromsaid cooling air flow, said air branching device being movable betweensaid first and second positions.
 4. A cooling fan system in accordancewith clam 1, wherein said at least one cooling fan is a pusher fanarranged upstream of said heat exchanger.
 5. A cooling fan system inaccordance with claim 4 and further comprising a housing disposedupstream of said heat exchanger, said at least one fan being connectedto said heat exchanger by means of said housing.
 6. A cooling fan systemin accordance with claim 1 and further comprising an air guiding housingarranged downstream of said heat exchanger directly adjacent the latter.7. A cooling fan system in accordance with claim 3, wherein said airbranching device is realized by adjustable plates, said adjustableplates having a first position permitting air moving through said heatexchanger to pass between them and a second position in which they closeagainst one another to supply air to said duct leading to said fuelcells.
 8. A cooling fan system in accordance with claim 7, wherein saidair guiding housing has a downstream side and said plates are arrangedat said downstream side.
 9. A cooling fan system in accordance withclaim 7, wherein said plates are arranged in the manner of a louverwindow.
 10. A cooling fan system in accordance with claim 7, whereinsaid plates are arranged in the manner of an iris diaphragm and have afirst state closed against one another in which they define a centralopening, said duct leading to said fuel cells having an entry and saidentry lying opposite to said central opening.
 11. A cooling fan systemin accordance with claim 7, wherein said plates are arranged in themanner of a roller shutter.
 12. A cooling fan system in accordance withclaim 6, and further comprising an air collecting box, said aircollecting box extending over a region of said air guiding housing notcovered in the air branching position by said air branching device andbeing adapted to collect air branched off by said air branching device,said duct leading to said fuel cells having a connection and said airbranched off by said air branching device being supplied to saidconnection.
 13. A cooling fan system in accordance with claim 12,wherein said air collecting box has a collecting aperture and whereinsaid air branching device is formed by a roller blind having a closedposition in which said roller blind adjoins said air collecting box, butdoes not close said collecting aperture.
 14. A cooling fan system inaccordance with claim 6, wherein said air guiding housing has an airoutlet side, wherein said air branching device is adapted to completelyclose off said air outlet side and wherein said air guiding housing hasa connection for said duct leading to said fuel cells.
 15. A cooling fansystem in accordance with claim 3, wherein a positioning motor isprovided, said positioning motor being attached to said air guidinghousing for the positioning of said plates.
 16. A cooling fan system inaccordance with claim 1 and further comprising a compressor having ahousing and adapted to feed oxygen to said fuel cells in normaloperation, wherein said duct leading to said fuel cells extends intosaid housing of said compressor.
 17. A cooling fan system in accordancewith claim 1, wherein said duct leading to said fuel cells leadsdirectly to said fuel cells.
 18. A cooling fan system in accordance withclaim 6, wherein an air filter is provided in said air collecting box.19. A cooling fan system in accordance with claim 1, wherein an airfilter is provided in said duct leading to said fuel cells.
 20. Acooling fan system in accordance with claim 1, wherein said cooling fan,said heat exchanger and said air branching device form a module.
 21. Acooling fan system in accordance with claim 5, said housing connectingsaid at least one fan to said heat exchanger having a connection forsaid duct leading to said fuel cells.
 22. A cooling fan system inaccordance with claim 1 and adapted for said cooling air flow to satisfyat least one further cooling task after passing through said heatexchanger prior to being discharged into an environment of said coolingfan system.
 23. A method for the operation of a fuel cell systemcomprising a plurality of fuel cells, a heat exchanger, at least onecooling fan adapted to produce a cooling air flow directed through saidheat exchanger and a compressor for feeding compressed air to said fuelcell arrangement, wherein at least a part of said cooling air flow issupplied to said fuel cells for the purpose of at least one of: startingthe fuel cell system operating; maintaining the operation of said fuelcells in a low load range during idling; maintaining the operation ofsaid fuel cells in a low load range during loss of speed by rolling; andmaintaining said fuel cells operating in a low load range during overrunoperation.
 24. A method in accordance with claim 22, wherein at least apart of said cooling air flow is also supplied to a reforming deviceconnected in front of said fuel cells.